This invention relates to an instantaneously tripping device operative upon closing a circuit interrupter.
Recent series overcurrent tripping devices for circuit interrupters are provided with long timing, short timing and instantaneous trip elements that are generally called three elements. These trip elements are selectively operative in response to the magnitude of a current flowing through the associated circuit interrupter. In general, the higher the current the shorter the time delay after which the circuit interrupters are arranged to be opened. For example, the trip element having the short timing characteristic is responsive to a flow of high current approximating a shortcircuiting current to open the associated circuit interrupter with a time delay corresponding to from several to several tens of cycles of the current. Such trip elements are used for selective interruptions. In brief, where a circuit interrupter has a load side divided into a multiplicity of branches each having connected thereto one circuit interrupter having a small capacity, the occurrence of a shortcircuiting fault at any one of terminal points results, of course, in the opening of a subordinate circuit interrupter disposed at that terminal point where the fault has occurred. Under these circumstances, if a master circuit interrupter operatively associated with that subordinate one would have been opened in response to the shortcircuiting fault then a multiplicity of trouble free branches connected to the same would be opened resulting in inconvenience. Therefore, if the master circuit interrupter is maintained in its closed position until the subordinate circuit interrupter has been opened or until after a time interval of from several to several tens of cycles of the current than the supply of electric power can continued without hindrance. This is because all the branches except for the branch having the fault occurring thereon are trouble free at a time point when the subordinate circuit interrupter has been opened.
Also, according to the type of circuit interrupters, the instantaneous trip element may be omitted from tripping devices by having the short timing region including even the interrupting current which should be properly imposed upon the associated circuit interrupter. This results in the necessity of imparting to circuit interrupters proper electrical and mechanical strengths sufficient to permit high currents such as a shortcircuiting current to flow therethrough during several tens of the cycles of current. In addition, the tripping devices not including the instantaneous trip element are required to perform the operation of completely closing the shortcircuited branch within the same time interval. Upon closing a shortcircuited branch, a very high electromagnetic repulsion is generated across the contacts involved. This leads to the necessity of increasing the electrical energy required to close the shortcircuited circuit against the high repulsion, beyond the required for the normal closing operation and also to the need of providing corresponding equipment. For example, a closing electromagnetic solenoid circuit be made larger. If such closing energy is insufficient then an electric arc will occur across the contacts at an inter-contact distance at which the closing force is balanced with the electromagnetic repulsion and during several tens of cycles of the current resulting in great damage to the contact units.